631 research outputs found
Novel multiple-band superconductor SrPt2As2
We present LDA calculated electronic structure of recently discovered
superconductor SrPt2As2 with Tc=5.2K. Despite its chemical composition and
crystal structure are somehow similar to FeAs-based high-temperature
superconductors, the electronic structure of SrPt2As2 is very much different.
Crystal structure is orthorhombic (or tetragonal if idealized) and has layered
nature with alternating PtAs4 and AsPt4 tetrahedra slabs sandwiched with Sr
ions. The Fermi level is crossed by Pt-5d states with rather strong admixture
of As-4p states. Fermi surface of SrPt2As2 is essentially three dimensional,
with complicated sheets corresponding to multiple bands. We compare SrPt2As2
with 1111 and 122 representatives of FeAs-class of superconductors, as well as
with isovalent (Ba,Sr)Ni2As2 superconductors. Brief discussion of
superconductivity in SrPt2As2 is also presented.Comment: 5 pages, 4 figure
Electronic Structure of New Multiple Band Pt-Pnictide Superconductors APt3P
We report LDA calculated band structure, densities of states and Fermi
surfaces for recently discovered Pt-pnictide superconductors APt3P
(A=Ca,Sr,La), confirming their multiple band nature. Electronic structure is
essentially three dimensional, in contrast to Fe pnictides and chalcogenides.
LDA calculated Sommerfeld coefficient agrees rather well with experimental
data, leaving little space for very strong coupling superconductivity,
suggested by experimental data on specific heat of SrPt3P. Elementary estimates
show, that the values of critical temperature can be explained by rather weak
or moderately strong coupling, while the decrease of superconducting transition
temperature Tc from Sr to La compound can be explained by corresponding
decrease of total density of states at the Fermi level N(E_F). The shape of the
density of states near the Fermi level suggests that in SrPt3P electron doping
(such as replacement Sr by La) decreases N(E_F) and Tc, while hole doping (e.g.
partial replacement of Sr with K, Rb or Cs, if possible) would increase N(E_F)
and possibly Tc.Comment: 5 pages, 5 figure
Twisted Masses and Enhanced Symmetries: the A&D Series
We study new symmetries between A and D type quiver gauge theories with
different numbers of colors. We realize these gauge theories with twisted
masses via a brane construction that reproduces all the parameters of the
Gauge/Bethe correspondence.Comment: 14 pages, 5 figure
Instanton counting, Macdonald function and the moduli space of D-branes
We argue the connection of Nekrasov's partition function in the \Omega
background and the moduli space of D-branes, suggested by the idea of geometric
engineering and Gopakumar-Vafa invariants. In the instanton expansion of N=2
SU(2) Yang-Mills theory the Nakrasov's partition function with equivariant
parameters \epsilon_1, \epsilon_2 of toric action on C^2 factorizes correctly
as the character of SU(2)_L \times SU(2)_R spin representation. We show that up
to two instantons the spin contents are consistent with the Lefschetz action on
the moduli space of D2-branes on (local) F_0. We also present an attempt at
constructing a refined topological vertex in terms of the Macdonald function.
The refined topological vertex with two parameters of T^2 action allows us to
obtain the generating functions of equivariant \chi_y and elliptic genera of
the Hilbert scheme of n points on C^2 by the method of topological vertex.Comment: 33 pages, 2 figures, (v2) minor changes, references added, (v3)
Comments and more references adde
A_{N-1} conformal Toda field theory correlation functions from conformal N=2 SU(N) quiver gauge theories
We propose a relation between correlation functions in the 2d A_{N-1}
conformal Toda theories and the Nekrasov instanton partition functions in
certain conformal N=2 SU(N) 4d quiver gauge theories. Our proposal generalises
the recently uncovered relation between the Liouville theory and SU(2) quivers.
New features appear in the analysis that have no counterparts in the Liouville
case.Comment: 23 pages. v2: some typos correcte
Electronic structure and possible pseudogap behavior in iron based superconductors
Starting from the simplified analytic model of electronic spectrum of iron -
pnictogen (chalcogen) high - temperature superconductors close to the Fermi
level, we discuss the influence of antiferromagneting (AFM)scattering both for
stoichiometric case and the region of possible short - range order AFM
fluctuations in doped compounds. Qualitative picture of the evolution of
electronic spectrum and Fermi surfaces (FS) for different dopings is presented,
with the aim of comparison with existing and future ARPES experiments. Both
electron and hole dopings are considered and possible pseudogap behavior
connected with partial FS "destruction" is demonstrated, explaining some recent
experiments.Comment: 5 pages, 4 figures, published versio
\Omega-deformation of B-twisted gauge theories and the 3d-3d correspondence
We study \Omega-deformation of B-twisted gauge theories in two dimensions. As
an application, we construct an \Omega-deformed, topologically twisted
five-dimensional maximally supersymmetric Yang-Mills theory on the product of a
Riemann surface and a three-manifold , and show that when
is a disk, this theory is equivalent to analytically continued Chern-Simons
theory on . Based on these results, we establish a correspondence between
three-dimensional superconformal theories and analytically
continued Chern-Simons theory. Furthermore, we argue that there is a mirror
symmetry between {\Omega}-deformed two-dimensional theories.Comment: 26 pages. v2: the discussion on the boundary condition for vector
multiplet improved, and other minor changes mad
Electronic states and magnetic excitations in LiV2O4: Exact diagonalization study
Motivated by recent inelastic neutron scattering experiment we examine
magnetic properties of LiV2O4. We consider a model which describes the
half-filled localized A1g spins interacting via frustrated antiferromagnetic
Heisenberg exchange and coupled by local Hund's interaction with the 1/8-filled
itinerant Eg band, and study it within an exact diagonalization scheme. In the
present study we limited the analysis to the case of the cluster of two
isolated tetrahedrons. We obtained that both the ground state structure and
low-lying excitations depend strongly on the value of the Hund's coupling which
favors the triplet states. With increasing temperature the triplet states
become more and more populated which results in the formation of non-zero
residual magnetic moment. We present the temperature dependence of calculated
magnetic moment and of the spin-spin correlation functions at different values
of Hund's coupling and compare them with the experimental results.Comment: 7 pages. 6 eps figure
Multiloop Superstring Amplitudes from Non-Minimal Pure Spinor Formalism
Using the non-minimal version of the pure spinor formalism, manifestly
super-Poincare covariant superstring scattering amplitudes can be computed as
in topological string theory without the need of picture-changing operators.
The only subtlety comes from regularizing the functional integral over the pure
spinor ghosts. In this paper, it is shown how to regularize this functional
integral in a BRST-invariant manner, allowing the computation of arbitrary
multiloop amplitudes. The regularization method simplifies for scattering
amplitudes which contribute to ten-dimensional F-terms, i.e. terms in the
ten-dimensional superspace action which do not involve integration over the
maximum number of 's.Comment: 23 pages harvmac, added acknowledgemen
A 5d/3d duality from relativistic integrable system
We propose and prove a new exact duality between the F-terms of
supersymmetric gauge theories in five and three dimensions with adjoint matter
fields. The theories are compactified on a circle and are subject to the Omega
deformation. In the limit proposed by Nekrasov and Shatashvili, the
supersymmetric vacua become isolated and are identified with the eigenstates of
a quantum integrable system. The effective twisted superpotentials are the
Yang-Yang functional of the relativistic elliptic Calogero-Moser model. We show
that they match on-shell by deriving the Bethe ansatz equation from the saddle
point of the five-dimensional partition function. We also show that the
Chern-Simons terms match and extend our proposal to the elliptic quiver
generalizations.Comment: 30 pages, 4 figures. v2: typo corrected, references adde
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